1. Technical Field
The present invention relates to image reading methods, image reading apparatuses, and storage media having a program stored thereon.
2. Related Art
Conventionally, so-called scanner devices are known that are image reading apparatuses for reading an image of a document surface. In these scanner devices, a document is placed on a platen constituted by a transparent glass plate or the like, a one-dimensional image sensor arranged across the platen scans along the surface of the document, and an image of the document surface is read by the image sensor.
The image sensor moves in a reciprocating manner along the platen and carries out an image-reading scan while moving in a forward pass from a home position, which is a movement commencement position. After image reading is finished, the image sensor moves back in a return pass toward the home position without carrying out a reading scan, then stops at the home position and stands by ready for the next image-reading scan.
Before commencing image reading, the scanner device carries out shading correction in order to standardize the sensitivity of each pixel of the image sensor. In order to carry out this correction, a white reference board whose uniform white color surface is arranged facing toward the image sensor side is arranged between the home position and the image reading commencement position. The scanner device is configured such that, before commencing image reading, shading correction is carried out by scanning the white color surface of the white reference board with the image sensor.
The image sensor is attached to a carriage and the image sensor moves in a reciprocating manner due to the carriage moving in a reciprocating manner by obtaining a driving force from a DC motor, which is a drive source, through a power transmission system constituted by components such as a gear train, pulleys, and a timing belt.
In this regard, so-called backlash occurs in the power transmission system constituted by components such as a gear train, pulleys, and a timing belt; the backlash originating in such factors as loose engagement of engaging portions between gears and slack in the timing belt. Backlash does not become a problem while the power transmission system continues to drive in a same direction since the components in the power transmission system (gear-to-gear, or pulley-to-timing belt) are being driven in a state in which a pressing force is constantly applied from a side that provides the driving force to a side that receives the driving force.
However, when the driving direction changes, for example, after a driving side gear of gears that are engaged with each other turns idly by a backlash amount, this gear engages with a receiving side gear and the driving force is transmitted.
The driving side gear rotates at high speed while turning idly by the backlash amount because it rotates in a light load state. And rotation of the gear on the receiving side of the driving force is stopped until the backlash from the driving side gear is eliminated. For this reason, the driving side gear commences engagement in a state in which it collides against the gear on the receiving side of the driving force. Consequently, immediately after engagement with the drive source side gear has commenced, the gear on the receiving side of the driving force also moves undesirably at high speed during a moment until the impact of the collision is absorbed.
A state in which the image sensor is standing by at the home position involves the image sensor stopping in a state having returned to the home position via a return pass after completion of image reading. For this reason, backlash is present in the drive transmission system in a direction in which the image sensor is to move to the forward pass side.
That is, for example, in the gears engaging with each other, when the driving side gear has rotated in the direction in which the image sensor moves, backlash is present in the gear that receives the driving force of that gear.
For this reason, if the image sensor commences to move by the rotation of the DC motor in this state, when backlash is eliminated, for example, when the drive source side gear and the drive force receiving side gear commence engagement, an impact is produced and the image sensor moves undesirably for a moment at high speed.
As means for addressing this problem means is conceivable for suppressing occurrences of impact of when eliminating backlash by setting rotation of the DC motor to low speed until the backlash is eliminated (JP-A-2005-237198).
However, when using the means described in Patent Document 1, there is a problem that the time until the image sensor commences movement is delayed.